Engine swap - Perkins 4-108 to replace Westerbeke 4-108

[World Spectator]

My aging 1976 Westerbeke 4-108 was rebuilt in the Bahama's 100 hours ago and still has too much grey smoke for my liking, I am looking at swapping the engine with a rebuilt Perkins 4-108 (1983) Same block but the water jacket, heat exchange unit and exhaust are very different - has anyone out there every had experience with this? The biggest problem seems to be the exhaust on the Perkins is exiting at the back rather than the front of the engine and needs to be modified. Did Perkins make a replacement unit that will allow the exhaust to exit via the front of the engine or can I swap  out the parts from the exhaust and heat exchanger parts from the Westerbeke and install them on the Perkins ? My Westerbeke also has an oil cooler and the Perkins does not, should this be a concern? Last option pull the Westerbeke and sleeve the pistons and check the values everything else is new.

[RayNWanda]

Perkins should have several exhaust configurations available, I would think.
Tell me more about the grey smoke. It could be a timing issue, it could be valve settings, or injectors. If the engine runs good and is not blue smoking, there is a good possibility it is a minor problem.